In 2020, there were 586,202 new cases of thyroid cancer worldwide, 448,915 in women and 137,287 in men. It was the ninth most frequent malignant tumor, excluding non-melanoma skin neoplasms [1].

The popularization of imaging tests such as cervical ultrasound and carotid Doppler increased the identification of asymptomatic thyroid nodules, including small tumors (‘incidentalomas’). When imaging criteria suggest malignancy [2], [3], treatment and follow-up (in most cases) are based on fine-needle aspiration (FNA) results. Although most thyroid nodules are benign, they can significantly cause patient anxiety. In these cases, FNA is the gold standard diagnostic modality [4]. It is a minimally invasive procedure accepted by patients; it provides rapid diagnosis, excellent cost-effectiveness, and high specificity for malignant lesions [5], [6].

According to the World Health Organization's classification of endocrine tumors, papillary thyroid carcinoma (PTC) accounts for almost 90 % of malignant thyroid neoplasms. Less frequently, there are cases of follicular carcinomas, medullary carcinomas, poorly differentiated carcinomas, and anaplastic carcinomas [7]. It is noteworthy that the various types of thyroid carcinomas present different morphologies because morphology influences the sensitivity and specificity of cytological examinations. Because PTC is the most prevalent histological type, morphology should be the primary focus of studies testing new tools to facilitate the diagnosis of thyroid malignancies.

In 2007, the Bethesda System for Thyroid Cytopathological Reports (TBSRTC) was established, and its second edition was updated in 2018. The TBSRTC proposes some morphological parameters that (in an appropriate clinical-radiological context) present accurate results and can guide follow-up. The following criteria should be highlighted: cellularity, amount of colloid, variation in nuclear size, presence of nuclear grooves, intranuclear pseudoinclusions, overlapping nuclei, microcalcifications, papillae, and proportion of follicular arrangements [8]. Moreover, no studies assess the relevance of each of these findings using a point score system that correlates with TBSRTC categories.

Therefore, this study aimed to create a point system based on cytomorphological criteria for evaluating FNA products from thyroid nodules to improve the accuracy of the TBSRTC's categories, increase the concordance among different services, and predict the risk of PTC. We hope this system will help cytopathologists identify the appropriate TBSRTC category of thyroid nodules, inform therapeutic decision-making, and aid diagnosis using a mobile telephone application.